4.1. Clinical Samples

Eight hundred two cases were submitted for diagnostic PD-L1 assessment as a reflex test over a 20 month period from four regional Northern Ireland hospitals (North, North-Western, South-Western, and Belfast Trusts) to the Regional Diagnostic Molecular Pathology Laboratory. Of the 802 cases, 99 were unsuitable for PD-L1 testing due to the sample containing <100 tumor cells or were, after central review, of an inappropriate cancer type. The remaining 703 NSCLC cases were reflex tested and had reports issued. Sample types included formalin fixed paraffin embedded (FFPE) blocks, bronchoscopic and core biopsies (n = 426), cytologies (n = 124), and surgical resections (n = 153). We have previously reported demographics for a large proportion of our lung cohort (564 cases) [5]. Additional whole slide images from our routine service were collected. Our cohort, from the same source of tissue samples, followed the exact same trends in terms of PD-L1 distribution and the key descriptors were the same, this is evidenced by the equivalent spread of the data in Figure 1. All cases were manually assessed and a consensus score reported by teams of two individuals who received training and are certified competent for clinical scoring of PD-L1 in NSCLC. To assess specificity and sensitivity, an intra-run reproducibility section from a four core tissue microarray was used in each test run, representing PD-L1 expression levels of <1%, 1–49% and >50%, as well as a positive control (tonsil). Stained tumor slides and blocks were retrieved and provided via the Northern Ireland Biobank, which has ethical approval to use de-identified tissue samples from the Belfast Health and Social Care Tissue Pathology archive (REC:11/NI/0013).